It is known to subject metals, in particular light metallic bodies such as, for example, aluminum strip wound into a coil, to a heat treatment for the purpose of improving the properties thereof, by means of blowing with hot gas jets issuing from nozzles in an annealing furnace. In the case of annealing furnaces usual up to now, the end faces of the stationary coil supported on charging machines are blown with hot gas jets from nozzles rigidly built into the furnace, which can lead to local overheating at the impingement points of the hot gas jets and to reduced heating of the material in the intermediate regions, and thus on the whole to nonuniform heating of the coil. The variable distribution of temperature and flow velocity inside the cross section of the hot gas stream has, as a necessary consequence, locally nonuniform heat transfer, which manifests itself in a nonuniform temperature distribution in the heat treatable material. In order to avoid partial overtemperature in the regions with the greatest heat transfer, the heat flux and thus the heating rate must not be too great. For this reason, the overtemperature as a function of the mean flow velocity of the hot gas must not exceed a critical value. What is more, in the case of annealing furnaces usual up to now, the coils are supported and remain supported on the charging machines or supports located inside the furnace during the heat treatment, which charging machines or supports are heated up by the hot gas stream at the same time, in a fashion undesirable per se, and cause slower heating of the regions of the coil lying in the wind shadow or heat shadow. Furthermore, as a consequence of the one-sided weight loading of the horizontally supported coil, deformations of the coil take place, by which means the unrolling of the aluminum strip can also be impaired on account of the unbalanced and out-of-round running, if one considers that a coil can have the weight of, for example, 30 tons and a diameter of, for example, 2.8 m.